Liquid desiccant air conditioner

ABSTRACT

A liquid desiccant air conditioner includes an absorption air conditioner and a liquid desiccant dehumidifier. The dehumidifier includes a liquid desiccant absorber for absorbing moisture contained in ambient air entering the dehumidifier, a boiler for boiling partially preheated dilute liquid desiccant to evaporate moisture to reconstitute the liquid desiccant into concentrated liquid desiccant, a first heat exchanger operable to transfer heat from the concentrated liquid desiccant to dilute liquid desiccant received from the desiccant absorber so as to raise the temperature of the dilute liquid desiccant to a first temperature, a condenser operative to receive partially heated dilute liquid desiccant from the first heat exchanger and receive steam generated by the boiler so as to sensibly heat the dilute liquid desiccant to a second temperature, and a second heat exchanger operable to transfer heat from concentrated liquid desiccant to the dilute liquid desiccant received from the condenser so as raise the temperature of the dilute liquid desiccant to a third temperature. The dilute liquid desiccant at the third temperature is directed to the boiler and the concentrated liquid desiccant from the second heat exchanger is directed to the first heat exchanger. A pump draws concentrated liquid desiccant from the boiler into the absorber. Steam from the boiler is also used to regenerate the refrigerant in the absorption air conditioner.

BACKGROUND

[0001] This is a continuation-in-part from application Ser. No.09/131,287, filed Aug. 7, 1998, which is a continuation-in-part fromSer. No. 08/984,741, filed Dec. 4, 1997, both of which are incorporatedherein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates generally to room air cooling anddehumidification, and more particularly, to a liquid desiccant airconditioner including a liquid desiccant dehumidifier which is energyefficient, corrosion resistant, and capable of operation with low energyusage.

DESCRIPTION OF THE PRIOR ART

[0003] Typical air conditioning units operate on a vapor compressioncycle. Over recent years, the phase out of CFC based air conditioningunits has been dictated by environmental concerns. One alternative tovapor compression units, is the absorption system. The basic elementsinclude an evaporator, condenser, absorber, pump, heat exchanger,throttle valve and regenerator. In the absorption cycle, an “absorbent”is used to absorb the refrigerant in the vaporized state after leavingthe evaporator. The vaporized refrigerant is converted back into theliquid phase in the absorber. Heat released in the absorption process isrejected to cooling water passed through the absorber. A solution ofabsorbent and refrigerant is pumped to a regenerator, where heat isadded and the more volatile refrigerant is separated from the absorbentthrough distillation. The refrigerant is then communicated to thecondenser, expansion valve and evaporator in a conventional manner. Aheat exchanger may be used for heat recovery between the absorbentreturned to the absorber and the absorbent refrigerant solutiondelivered to the regenerator.

[0004] Absorption systems currently represent only a small percentage ofcommercial refrigeration systems because they are generally bulky andinefficient. However, with concerns over CFCs and ever increasing energycosts, the absorption unit has potential to provide efficient cooling bytaking advantage of waste heat. This may be provided by combining suchan absorption unit with a liquid desiccant dehumidifier.

[0005] It is known in the art to dehumidify ambient air using liquiddesiccant systems. These devices typically utilize hygroscopic liquidssuch as lithium bromide (LiBr), lithium chloride (LiCI) or calciumchloride (CaCl2) as the desiccant solution. In a desiccant system, thedesiccant solution absorbs moisture from ambient air exposed to thesolution. As the desiccant solution continues to absorb moisture, itbecomes dilute and must be regenerated. In the regeneration process, thedesiccant solution is heated to evaporate the excess moisture or thedesiccant solution is brought into contact with a hot gas to desorb theexcess moisture. In some expedients, air regenerators are used toregenerate the desiccant. These arrangements have relatively highoperating costs as energy is required to provide a source of heat and togenerate a suitable flow of air. In others, boiler-type regenerators areemployed. However, boiler embodiments are expensive, as the corrosivenature of liquid desiccant solutions necessitates the use of costlycorrosion resistant metals.

[0006] A liquid desiccant dehumidification system in which a liquiddesiccant is regenerated with a boiler is described in U.S. Pat. No.4,939,906 (“the '906 patent”). The '906 patent discloses a gas-fireddesiccant boiler and a combined desiccant regenerator/interchange heatexchanger in which the combined regenerator/heat exchanger utilizessteam produced from the boiler to provide heat for partial regeneration.The desiccant boiler has a liquid/vapor separator chamber andthen-nosyphon recirculation to reduce scale and corrosion of the boiler.Specifically, the overall system is shown in FIG. 1, wherein outdoor airis drawn into the system through an inlet duct 22, and is evaporativelycooled by a water spray 24. The cooled air is directed to a desiccantconditioner 26 to which return air is also directed through a duct 30.In the desiccant conditioner 26, the return air is contacted with aliquid desiccant solution from a sprayer 28. The desiccant liquid isdisclosed as lithium calcium chloride.

[0007] This dehumidified air is then supplied to the space to bedehumidified, or it can be sensibly cooled through an evaporative cooler32. The desiccant dehumidifies the air stream, and in the process itsmoisture-absorbing capability is reduced. This capability is regeneratedby passing a portion of the dilute desiccant from the conditioner 26 toa first interchange heat exchanger 44 wherein the temperature of thedesiccant is raised. The weakened desiccant is partially concentrated inan air-desiccant regenerator 46 in which heated air from a regenerationair heater 48 contacts the liquid desiccant. This desiccant is pumpedthrough a second interchange heat exchanger 52 and thereafter to adesiccant boiler 56 in which regeneration of the desiccant is completed.The water vapor generated in the desiccant boiler 56 raises thetemperature of the air passing through the regeneration air preheater48. The interchange heat exchangers 44, 52 reduce the temperature of theregenerated desiccant as it returns along the pipe 60 to the conditioner26.

[0008] The boiler 56 is depicted in FIG. 2 and operates on naturalcirculation, with the density of the fluid (part liquid, part vapor) inthe “fired” tubes 70 being less than the density of the liquid in theouter “unfired” tube 74. A porous ceramic burner 80 facilitatescombustion to provide a heat source, and hot combustion gases are blownthrough a combustion chamber formed by a housing 88 enclosing the firedtubes 70 so as to effect flow across fins 90 of the fired tubes 70. Weakdesiccant is pumped into the fired tubes 70 through a manifold 94 whichcauses water in the desiccant to be vaporized. Accordingly, a densitydifferential is created between the fluid in the fired tubes 70 and theunfired tubes 74 connected between the manifold 94 and a liquid/vaporseparator 98 outside the combustion chamber housing 88. This densitydifferential induces a natural flow of desiccant solution up the firedtubes 70 and down the unfired tubes 72. In this manner, the naturalcirculation of desiccant keeps the inside walls of the fired tubes 70coated with desiccant to thereby reduce or prevent “hot spots” fromforming on the inside of the fired tubes 70 to reduce corrosion andscale build up in the fired tubes 70.

[0009] The liquid vapor separator 98 at the top of the boiler 56separates water vapor from the concentrated liquid desiccant. A portionof the concentrated desiccant is withdrawn from the bottom of theliquid/vapor separator 98 and is returned to the desiccant conditioner26. Water vapor flowing out of the top of the liquid/vapor separator 98is subsequently condensed to heat air for use in an earlier regenerationstep shown in FIGS. 3 and 4.

[0010] The combined regenerator/interchange heat exchanger, depicted inFIGS. 3 and 4, comprises two (2) interchange heat exchangers 44, 52, thedesiccant regenerator 46 and the regeneration air heater 48. Thecombined desiccant regenerator/interchange heat exchanger is identifiedby the reference numeral 102, and is constructed by alternately stackingtwo (2) different corrugated plates (see FIG. 4) to define alternatingflow channels. Water vapor or steam from the desiccant boiler 56 isintroduced near the top of the regenerator/exchanger 102 in alternatechannels (plate A). This water vapor is condensed, thereby transferringheat to the air and weak desiccant entering adjacent channels near thetop of the regenerator/heat exchanger 102 (plate B). The upper portionof each plate corresponds to the desiccant regenerator 46 andregeneration air heater 48. As the water vapor condenses, the weakdesiccant and air mixture is heated and the desiccant is partiallyregenerated. Warm air and moisture are exhausted by fan 106 to theoutdoors. An entrainer 108 is provided to prevent desiccant fromescaping the combined regenerator/exchanger 102. The partiallyregenerated desiccant flows into the middle of a channel plate B, and isfurther heated by the hot concentrated desiccant removed from theliquid/ vapor separator 98. Hot concentrated desiccant from the boiler56 is introduced at the middle of plate A while the partiallyregenerated desiccant is removed from the middle of plate B. Thepartially regenerated desiccant is then pumped to the desiccant boiler56. Diluted desiccant from the regenerator/heat exchanger 102 isintroduced at the bottom of the plate A and is heated by the hotdesiccant from the boiler 56. The heated dilute desiccant from theregenerator/heat exchanger 102 is then removed from the center of plateB and pumped to the top of plate B.

[0011] The apparatus shown and described in the '906 patent exhibitsseveral disadvantages. The regeneration process described thereinrequires the flow of hot air through the system in order to operate.This necessitates the use of additional components such as fans, airpreheaters, and liquid/vapor separators, which adds system complexity.Furthermore, the multiple stacked plate interchange heat exchangerconfiguration is complex and takes up a relatively large amount ofspace.

[0012] The present invention provides an improved air cooling systemcomprising an absorption air conditioner operating in conjunction with aliquid desiccant dehumidifier.

SUMMARY OF THE INVENTION

[0013] One of the primary objects of the present invention to provide aliquid desiccant air conditioner which dehumidifies and cools ambientair in a combined liquid desiccant dehumidifier and refrigerantabsorption cycle.

[0014] Another object of the present invention to provide a highlyefficient liquid desiccant air conditioner which does not require CFCs.

[0015] Still another object of the present invention to provide a liquiddesiccant air conditioner which does not require a compressor or anyexternal heat input to effect regeneration of the refrigerant absorbent.

[0016] Still another object of the present invention to provide a liquiddesiccant air conditioner which utilizes primarily plastic components toprevent corrosion.

[0017] Another object of the present invention to provide a liquiddesiccant air conditioner in which steam to desiccant heat recoverytakes place in a condenser, and wherein lightweight corrosion resistantcomponents are used for the interchange heat exchangers.

[0018] A feature of the present invention lies in the provision of aliquid desiccant air conditioner in which the waste heat radiating fromthe boiler is utilized in an interchange heat exchanger for desiccantregeneration.

[0019] Another feature of the present invention lies in the provision ofan absorber employing a plurality of stacks of desiccant absorber padsarranged to provide improved air distribution and reduce channeling orshort circuiting of air flow through the absorber.

[0020] Another feature of the present invention lies in the provision ofa boiler configured to provide a relatively long flow path betweendesiccant inlet and outlet ends so as to reduce mixing of hotconcentrated desiccant with cold diluted desiccant, thereby increasingthe efficiency by reducing the mass of the desiccant required to bemaintained at the highest temperature in the boiler.

[0021] Still another feature of the present invention lies in theprovision of a coiled condenser having sidewalls defining at least onesteam flow channel, and a convoluted desiccant flow tube extendingthrough each channel so as to achieve a high heat transfer coefficientin a compact low cost construction.

[0022] Another feature of the present invention lies in the provision ofa liquid desiccant air conditioner which is lightweight, energyefficient, and inexpensive to manufacture.

[0023] In accordance with the foregoing objects and features, thepresent invention provides a liquid desiccant air conditioner thatincludes a liquid desiccant dehumidifier and an absorption airconditioner. The dehumidifier includes and absorber for absorbingmoisture contained in ambient air entering the dehumidifier and passingthrough the desiccant absorber. The desiccant absorber constructed andarranged for receiving concentrated liquid desiccant and dispensingdilute liquid desiccant. A boiler operates to boil partially preheateddilute liquid desiccant to evaporate moisture and reconstitute theliquid desiccant into concentrated liquid desiccant. A condenserreceives steam generated by the boiler, and receives dilute liquiddesiccant from the absorber. The condenser sensibly heats the diluteliquid desiccant therein by recovering the latent heat of condensationas steam from the boiler is condensed, to thereby increasing operatingefficiency by preheating the dilute liquid desiccant prior to deliveryto the boiler.

[0024] The liquid desiccant dehumidifier includes a first heat exchangeroperable to transfer heat from the concentrated liquid desiccant todilute liquid desiccant received from the desiccant absorber to raisethe temperature of the dilute liquid desiccant to a first temperature.The condenser in the dehumidifier receives partially heated diluteliquid desiccant from the first heat exchanger at the first temperature.The condenser sensibly heats the dilute liquid desiccant therein to asecond temperature by recovering the latent heat of condensation assteam from the boiler is condensed. A second heat exchanger in thedehumidifier communicates with the condenser, the boiler and the firstheat exchanger. The second dehumidifier heat exchanger receivesconcentrated liquid desiccant from the boiler and receives dilute liquiddesiccant from the condenser at the second temperature. The second heatexchanger raises the temperature of the dilute liquid desiccant to athird temperature after which the dilute liquid desiccant at the thirdtemperature is passed to the boiler and the concentrated liquiddesiccant from the second heat exchanger passes to the first heatexchanger. A pump effects flow of concentrated liquid desiccant into theabsorber.

[0025] An evaporator operative to cool dehumidified air received fromthe dehumidifier absorber. A refrigerant is vaporized in the evaporatorand passes to a refrigerant absorber that contains an absorbent solutionsuch as, for example, ammonia-water or water-lithium bromide. Therefrigerant-absorber solution is pumped to a regenerator in which therefrigerant is separated from the absorbent. The regenerator receivessteam from the boiler as a heat input to effect regeneration. Arefrigerant condenser receives the reconstituted refrigerant from theregenerator after which the refrigerant passes through an expansionvalve into the evaporator in a conventional manner. A heat exchanger maybe used in the absorption air conditioner to recover heat from theabsorbent as it is returned to the refrigerant absorber so as to preheatthe refrigerant-absorbent solution prior to introduction of the solutioninto the regenerator.

[0026] The desiccant absorber includes at least two horizontallyarranged generally equal length termed stacks, of relatively closelyspaced vertically disposed microglass fiber plates. The stacks aredisposed in parallel spaced relation so that the plates of each row aregenerally coplanar with corresponding plates of the other row. A gap isprovided between mutually opposed vertical marginal edges of the platestacks. Concentrated desiccant is introduced into the desiccant absorberfrom a horizontal microglass fiber plate at the top of the stacks sothat the desiccant wicks into the distribution plate and down thevertical fiber plates. A drain pan for collecting the dilute desiccantdisposed at the bottom of the desiccant absorber. Ambient air is drawnthrough the absorber so as to contact the exposed faces of the plates.The air mixes as it passes through the gap between the stacks so as toimprove air distribution and reduce channeling or short circuitry withan improvement in the distribution of mass transfer driving force and anincrease in mass transfer coefficient to increase the absorptioncapacity.

[0027] The various components are disposed with respect to one anotherto take advantage of gravity feed to communicate the liquid desiccantfrom the absorber to the boiler via the first and second heat exchangersand the condenser, thereby eliminating the need for multiple pumps inthe system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In accordance with the above, the present invention will now bedescribed in detail with particular reference to the accompanyingdrawings.

[0029]FIG. 1 is a schematic of a first embodiment of a liquid desiccantair conditioner in accordance with the present invention;

[0030]FIG. 2 is a schematic of a second embodiment of a liquid desiccantair conditioner in accordance with the present invention;

[0031]FIG. 3 is a schematic of a third embodiment of a liquid desiccantair conditioner in accordance with the present invention;

[0032]FIG. 4 is a schematic of a fourth embodiment of a liquid desiccantair conditioner in accordance with the present invention;

[0033]FIG. 5 is a schematic of a fifth embodiment of a liquid desiccantair conditioner in accordance with the present invention;

[0034]FIG. 6 is a schematic of a sixth embodiment of a liquid desiccantair conditioner in accordance with the present invention;

[0035]FIG. 7 is a schematic of a seventh embodiment of a liquiddesiccant air conditioner in accordance with the present invention;

[0036]FIG. 8 is an exploded isometric view of the portable liquiddesiccant dehumidifier in accordance with the present invention;

[0037]FIG. 8A is a block diagram depicting the general operation of theliquid desiccant dehumidifier;

[0038]FIG. 9 is an exploded isometric view of a desiccant absorberassembly;

[0039]FIG. 9A is a detail view of the microglass fiber plates in theabsorber;

[0040]FIG. 9B is a side elevational view of a desiccant absorber inanother embodiment;

[0041]FIG. 9C is a detail view of the absorber pads;

[0042]FIG. 9D is an isometric view of the desiccant absorber of FIG. 9B;

[0043]FIG. 10 is an isometric view of a boiler;

[0044]FIG. 11 is an isometric view of a coiled interchange heatexchanger and the boiler;

[0045]FIG. 11A is an isometric view of a boiler in an alternativeembodiment;

[0046]FIG. 12 is an isometric view of a split interchange heatexchanger;

[0047]FIG. 12A is a plan view of an inner tube for an interchange heatexchanger having a convoluted profile;

[0048]FIG. 12B is a plan view of an inner tube for an interchange heatexchanger having a corrugated profile;

[0049]FIG. 13 is an isometric cut-away view of a condenser in a firstembodiment;

[0050]FIG. 14 is an isometric cut-away view of an inner shell of thecondenser shown in FIG. 13;

[0051]FIG. 15 is an isometric cut-away view of a condenser in a secondembodiment;

[0052]FIG. 16 is an isometric cut-away view of a condenser in a thirdembodiment;

[0053]FIG. 17 is an isometric view of a condenser in a fourthembodiment;

[0054]FIG. 18 is an isometric view of a condenser is a fifth embodiment;

[0055]FIG. 19 is an isometric cut-away view of a frame for housing therespective components of the system;

[0056]FIG. 20 is an isometric cut-away view depicting the frame and someof the components installed therein; and

[0057]FIG. 21 is an exploded perspective view of an alternativeembodiment of a liquid desiccant dehumidifier in accordance with thepresent invention;

[0058]FIG. 22 is a plan view of the absorber illustrated in FIG. 21 butwith the top plate removed to illustrate the gap between the two stacksof absorber plates for improved distribution of mass transfer resultingfrom passive mixing of air within the gap;

[0059]FIG. 23 is a front elevational view of the absorber illustrated inFIG. 22;

[0060]FIG. 24 is a perspective view of the boiler and associatedinterchange heat exchanger of FIG. 21 but with the outer shell orhousing removed for clarity;

[0061]FIG. 25 is a plan view of the boiler and associated coilinterchange heat exchanger illustrated in FIG. 24, portions being brokenaway for clarity;

[0062]FIG. 26 is a transverse sectional line taken substantially alongline 26-26 of FIG. 25;

[0063]FIG. 27 is a perspective view of the coiled condenser of FIG. 21with the top plate removed to show the internal convoluted tube throughwhich desiccant is passed; and

[0064]FIG. 28 is an enlarged detail view, taken within the line 28-28 ofFIG. 27.

DETAILED DESCRIPTION

[0065] Referring now to the drawings, FIGS. 1-7 schematically illustratevarious embodiments of a liquid desiccant air conditioner (“LDA”),generally characterized by the reference numeral 10.

[0066]FIG. 1 is a schematic diagram of a first embodiment of the LDA 10that includes a liquid desiccant dehumidifier 200 and an absorption airconditioner 202. The liquid desiccant dehumidifier 200 illustrated inFIG. 8 includes an absorber 12, a condenser, 86, and a boiler 34. Aninterchange heat exchanger 58 is disposed between boiler 34 andcondenser 86, and a split interchange heat exchanger 66 is disposedbetween condenser 86 and absorber 12.

[0067] The liquid desiccant dehumidifier 200 dehumidifies incomingambient air prior to effecting sensible cooling of the air in theabsorption air conditioner 202. The absorption cycle employs waste heatgenerated by the boiler 34 of liquid desiccant dehumidifier 200 forenergy efficient cooling and dehumidification. The air conditioner 202operates on a conventional absorption cycle, and includes an absorber204, a pump 206, a heat exchanger 208, a throttle valve 210, aregenerator 212, an evaporator 214, a condenser 216, and an expansionvalve 218. In the absorption cycle, an absorbent, such as aqueousammonia or aqueous lithium bromide, is used to absorb refrigerant in thevaporized state after leaving evaporator 214. The vaporized refrigerantis absorbed back into the liquid phase in absorber 204. Heat released inthe absorption process is rejected to cooling water or air passedthrough absorber 204. A solution of absorbent and refrigerant is pumpedto regenerator 212, where heat is added and the more volatilerefrigerant is separated from the absorbent. The refrigerant is thencommunicated to condenser 216, through expansion valve 218 and into theevaporator 214 in a conventional manner. A heat exchanger 208 may beused for heat recovery between the warm absorbent returned to theabsorber 204 through throttle valve 210, and the absorbent-refrigerantsolution delivered from the absorber 204 to the regenerator 212 via pump206. The regenerator 212 fluidly communicates with boiler 34 to receivesteam generated in reconstituting the liquid desiccant as describedbelow. In this manner, no external heat input is required to regeneratethe refrigerant. The heat exchanger 208 can be configured as describedbelow with respect to interchange heat exchanger 66 of the liquiddesiccant dehumidifier 200.

[0068]FIG. 2 is a schematic diagram illustrating a second embodiment ofthe LDA 10 which adds an indirect evaporative cooler 220 for cooling theincoming air with exhaust air from the residence prior to passing theincoming air through the desiccant absorber 12. The indirect evaporatorcooler 220 receives a water supply from condenser 86 and regenerator212. Fresh air is directed into the cooler 220 from the ambient, cooled,and thereafter delivered to desiccant absorber 12. The remainder of thecycle operates as described in respect to the embodiment of FIG. 1.

[0069]FIG. 3 is a schematic diagram illustrating a third embodiment ofthe LDA 10 which adds a direct evaporative cooler 222 to the embodimentof FIG. 2. The direct evaporative cooler 222 is operative to furthercool the air prior to delivery to the ambient. Water is supplied tocooler 222 from condenser 86 and regenerator 212. FIG. 4 schematicallyillustrates a fourth embodiment of the LDA 10 in which the ambient airis first directed into the absorber 12 for dehumidification, and theninto the indirect evaporative cooler 220 for cooling. FIG. 5 is aschematic diagram illustrating a fifth embodiment of the LDA 10 which issimilar to that shown in FIG. 1, but adds the direct evaporative cooler222.

[0070]FIG. 6 schematically illustrates a sixth embodiment of the LDA 10which does not utilize a refrigerant. In this expedient, the LDA 10cooperates with an indirect evaporative cooler 220 and a directevaporative cooler 222 to cool and dehumidify the incoming air. The airis directed through indirect evaporative cooler 220, cooled, andthereafter delivered to the desiccant absorber 12. The dehumidified airis then passed through the direct evaporative cooler 222 where it isfurther cooled by sensible cooling and exhausted to the ambient. Theprinciple of operation is generally the same as described in respect tothe embodiments of FIGS. 1-5. Water from condenser 86 is delivered toindirect evaporative cooler 220 and direct evaporative cooler 222.Exhaust air from the residence is communicated to the indirectevaporative cooler 220. FIG. 7 is a schematic diagram illustrating aseventh embodiment of the LDA 10 which is similar to that shown in FIG.6 and described above, except that the incoming ambient air is firstdehumidified in the desiccant absorber 12 and thereafter cooled in theindirect evaporative cooler 220.

[0071] Referring now to FIGS. 8 and 8A, the desiccant dehumidifiersection 200 includes liquid desiccant absorber 12 for absorbing moisturecontained in air entering air conditioner 10 and passing throughdesiccant absorber 12. The desiccant absorber 12 is constructed andarranged for receiving concentrated liquid desiccant at the top ofdesiccant absorber 12 and dispensing dilute liquid desiccant from thebottom of desiccant absorber 12. The desiccant solution may be any oneof several conventional solutions, including aqueous LiBr, LiCl or CaCl,as described above, or any mixture of these solutions. Referring toFIGS. 9 and 9A, desiccant absorber 12 includes a distributor 14 disposedat the top of desiccant absorber 12 which receives concentrated liquiddesiccant and delivers the liquid desiccant through a plurality of“spaghetti” tubes 16 extending radially outward from a central hub 18.The desiccant absorber 12 includes a plurality of horizontally andvertically disposed interconnected microglass fiber plates. The verticalplates are identified by reference numeral 20, and are supported byhorizontal interconnecting fiber plates 22 as shown. The top plate 22 isreferred to as a distribution sheet. The concentrated desiccant wicksinto the distribution sheet 22 and down the vertical plates 20. Thevertical plates 20 contain beads 21 which separate and support adjacentvertical plates 20. Ambient air is drawn into the unit and forcedthrough the microglass fiber plates by a fan 23 (FIG. 8) so thatmoisture in the air is removed as the air makes contact with the liquiddesiccant. As the desiccant dehumidifies the air stream, themoisture-absorbing capability of the desiccant is reduced and thedesiccant must be regenerated. The dilute desiccant is collected in adrain pan 24 disposed at the bottom of desiccant absorber 12. The drainpan 24 includes an intermediate support plate 26 defining at least onedrain hole 28 which enables the dilute desiccant to flow into a bottomchamber defined between support plate 26 and a bottom wall 30 of drainpan 24. A drain tube 32 including a one-way or check valve 33 extendsfrom the bottom chamber to direct the dilute desiccant out of absorber12. The absorber components are disposed within a frame 35 as shown inFIG. 19, which can be fabricated from materials including, but notlimited to, polypropylene, polyethylene, Teflon, polyvinylidenefluoride, polycarbonate, PVC or polystyrene. The frame 35 includes aplurality of shelves 37 a, 37 b, and 37 c for supporting the respectivecomponents of the unit described below.

[0072] In an alternative embodiment of the absorber shown in FIGS.9B-9D, a plurality of absorber pads 20 a are stacked side-by-side andbonded together at the ends with an adhesive “A” (or taped) so that thegaps between the pads 20 a are completely sealed to force the liquiddesiccant to wick through the pads 20 a. The pads 20 a are received inan aperture or slots in a top tray or distributor pan 25 and a bottomtray or drain pan 27. Any gaps between the pads 20 a and the pans 25, 27may be filled with an RTV silicone sealant or like material. Liquiddesiccant is communicated into the distributor pan 25 through an inlet29. This configuration prevents the liquid desiccant from just flowingover the surface of the pads, and consequently increases absorberefficiency. The trays 25, 27 effectively prevent spillage of liquiddesiccant from the absorber 12 in the event of tilting. In addition, theliquid desiccant supplied to the distributor pan 25 forms a thin film onthe pan surfaces to reach every distributor pad 20 a to improvedesiccant distribution.

[0073] The dilute liquid desiccant is regenerated into concentrateddesiccant by boiling the liquid desiccant in a boiler 34 at atemperature in the range of from approximately 260° F. to 320° F. Animprovement over prior art systems resides in the use of steam todirectly preheat the dilute liquid desiccant. The dilute liquiddesiccant is thus passed through a condenser and preheated using thelatent heat of condensation of the steam produced by boiling the liquiddesiccant. Preferably, a series of interchange heat exchangers areemployed to further preheat the dilute liquid desiccant entering theboiler 34 by recovering heat from the concentrated liquid desiccantdelivered to absorber 12 from boiler 34 to further increase operatingefficiency. These components are described in more detail below.

[0074] Referring to FIG. 10, the boiler 34 is configured in the shape ofa tub or vessel having an elongated horizontal dimension. The horizontalelongation provides a uniform temperature gradient, and thus a uniformconcentration level of the liquid desiccant solution, as compared to avertically elongated boiler. The boiler 34 includes side walls 36, abottom wall 38, a top wall 40, and a peripheral support flange 42. Theboiler 34 is constructed from materials including, but not limited to,polycarbonate, polyvinylidene fluoride, Teflon, fiber glass and thelike. A heating element 44 is coiled proximal to the bottom wall 38 asshown, and is connected to a pair of leads 46 in a conventional manner.A thermocouple 48 extends into boiler 34 to monitor the internaltemperature. The leads 46 and thermocouple 48 extend through top wall40. The heating element 44 and thermocouple 48 are operable associatedwith a controller (not shown) for maintaining boiler 34 at the optimumtemperature. A pair of steam outlets 50 extend through top wall 40 todeliver steam generated by boiling the liquid desiccant to a condenserdescribed in more detail below.

[0075] Referring to FIG. 11, a drain tube 51 is coupled to one of theside walls 36 to enable boiler 34 to be emptied as required. A U-fitting52 is coupled to the upper region of one of the side walls 36 to receivepreheated dilute liquid desiccant from the condenser through an inletport 54, and to dispense concentrated liquid desiccant through an outletport 56. The U-fitting 52 communicates with a coiled interchange heatexchanger 58, which comprises at least one tube assembly including aninner tube 60 concentrically disposed within an outer tube 62 to definean annulus 64 therebetween. The tube assembly is coiled around boiler 34to recover the waste heat radiating through side walls 36. Thisarrangement is exemplary, as the tube assembly could be embedded withinthe side walls 36, or disposed in contact with top wall 40. Theconcentrated liquid desiccant from boiler 34 enters the annulus 64through side wall 36 and is directed to outlet port 56. The partiallyheated dilute liquid desiccant from the condenser is passed through theinner tube 60 in a direction counter to the concentrated liquiddesiccant and enters boiler 34 through side wall 36. Alternatively, theconcentrated liquid desiccant is passed through inner tube 60 and thedilute liquid desiccant is passed through annulus 64. The inner tube 60is preferably fabricated from Teflon and outer tube 62 is constructedfrom silicone rubber. The Teflon inner tube 60 has relatively high heatconductivity, while the outer silicone rubber tube 62 has a relativelylow thermal conductivity and is a good insulator. These components canwithstand relatively high temperatures (−400° F.), and are not corrodedby the desiccant solution. To improve efficiency, inner tube 60 may beconvoluted as shown in FIG. 12A or corrugated as shown in FIG. 12B. Itwill be understood that the use of this type of Teflon/silicone rubbertube-in-tube heat exchanger is not limited to a liquid desiccant system.There are many applications in which this arrangement may be employed.The particular operation of the coiled interchange heat exchanger 58will be described in more detail below.

[0076]FIG. 11A is an isometric view of a boiler 34 a in an alternativeembodiment, having a double-wall configuration including an inner wall400 and an outer wall 402 which define an inner vessel 404 and an outervessel 406. A heating element 408 extends into the inner vessel 404 andaround the floor as shown. The incoming liquid desiccant from condenser86 enters the outer vessel 406 of the boiler at inlet 410. Hot liquiddesiccant from the inner vessel 404 is communicated into pipe 412 whichcoils through the outer vessel 406 to effect heat transfer with theincoming liquid desiccant. The desiccant puddle contained in the outervessel 406 is heated and the hottest portion of the liquid is forced torise to the top of the vessel 406. It is then fed into the inner vessel404 via an inlet 414. A thermocouple 416 is disposed in the inner vessel404 as described above to control the boiler temperature. Thisarrangement forces any heat radiated or conducted from the inner vessel404 to flow through the desiccant puddle in the outer vessel 406,thereby reducing thermal losses and pressure losses attributable to longflow paths. The heating element 408 is disposed below the pump suctionor inner vessel boiler outlet 415 a so that heating element 408 isalways immersed in a pool of liquid desiccant within the inner vessel404. In this manner, the pump 80 stops drawing liquid desiccant frominner vessel 404 before it is reduced to a level beneath the heatingelement 408. Hot liquid desiccant leaves the boiler through outlet 415b. This arrangement eliminates the need for a low-level control switch.High level control in the boiler is necessary to provide consistentdehumidification and to prevent excess liquid buildup. A high levelcontrol switch can be eliminated by sizing the inner vessel 404 with aninternal volume equal to approximately twice the volume of pooled liquiddesiccant accumulation. This takes advantage of the inherent desiccantproperties to make the system flexible to adapt to varying weatherconditions without compromising performance.

[0077]FIG. 12 depicts a split interchange heat exchanger 66 thatincludes a pair of tube assemblies 68. Each tube assembly 68 comprisesan inner tube 70 concentrically disposed within an outer tube 72 todefine an annulus 74 therebetween. The dilute liquid desiccant fromdesiccant absorber 12 is gravity fed to the interchange heat exchanger66 where it is directed through a manifold 76 and into the inner tubes70. Concentrated liquid desiccant from boiler 34 is first deliveredthrough coiled interchange heat exchanger 58 and thereafter directedthrough a U-fitting 78 coupled to the respective outer tubes 72 and intothe annuli 74. Alternatively, dilute liquid desiccant is passed throughannuli 74 and concentrated liquid desiccant is passed through innertubes 70. In this manner, heat is transferred from the concentratedliquid desiccant to the dilute liquid desiccant within split interchangeheat exchanger 66. The concentrated liquid desiccant is thereafter drawninto a pump 80 (FIGS. 8 and 8A) through a U-fitting 82 coupled to therespective outer tubes 72. The pump 80 delivers the concentrated liquiddesiccant to distributor 14 of absorber 12. The partially heated diluteliquid desiccant flows through a manifold 84 to the condenser. Duringthis stage, the dilute liquid desiccant dispensed from absorber 12 israised to a first temperature. As discussed above with respect to coiledinterchange heat exchanger 58, the inner tubes 70 may be fabricated fromTeflon and the outer tubes 72 may be constructed from silicone rubber.Likewise, the inner tubes may be provided with a convoluted orcorrugated profile as shown in FIGS. 12A and 12B, respectively.

[0078] The partially heated liquid desiccant at the first temperature isdelivered to a condenser 86 from split interchange heat exchanger 66 asshown in FIGS. 8 and 8A. FIGS. 13 and 14 illustrate a first embodimentof condenser 86 which is comprised of an inner shell 88 disposed withinan outer housing 90 defining at least one chamber 92 between inner shell88 and housing 90. The housing 90 includes a plurality of side walls 94,a top wall 96 and a bottom wall 98. A pair of steam tubes 100communicate with inner shell 88 through top wall 96 to deliver steamfrom boiler 34. A pair of air vents 102 likewise communicate withchamber 92 through top wall 96 to evacuate excess air therefrom. Acondensate tube 104 communicates with inner shell 88 through bottom wall98 to drain condensate into a condensate pan 106 (FIG. 8A). An inlettube 108 communicates with chamber 92 through one of the side walls 94to deliver partially heated dilute desiccant to condenser 86 from splitinterchange heat exchanger 66. An outlet tube 110 is similarly disposedto communicate with chamber 92 on an opposite side of condenser 86 todeliver dilute desiccant which is sensibly heated to a secondtemperature by the latent heat of condensation as the steam condenses inthe inner shell 88, to the coiled interchange heat exchanger 58 via theinlet port 54 of U-fitting 52 shown in FIGS. 8 and 11. A fraction of thedesiccant flow leaving the condenser may be recirculated to thedesiccant absorber 12. This reduces the flow rate to the boiler 34 tolower heat loss and increase energy efficiency. In addition, thismaintains a relatively high flow through the absorber 12 and condenser86 to yield a higher absorption and condensation capacity. To facilitateheat transfer, inner shell 88 is fabricated from materials includinginconel, monel, titanium, Teflon, Teflon-coated copper, Teflon-coatedaluminum, and Teflon-coated stainless steel. The housing 90 ispreferably fabricated from materials including Teflon, polycarbonate,polyvinylidene fluoride, polypropylene, silicone rubber, polyethylene,and polystyrene. If a plastic such as Teflon is used for the housing 90,the wall thickness is made suitably thick to provide the necessaryinsulating properties.

[0079] The condenser 86 may incorporate a plurality of fins 112 locatedon the exterior of inner shell 88 and a plurality of fins 114 disposedon bottom wall 98 of housing 90. The inner shell 88 may be provided witha plurality of baffles 116 to prevent short circuiting from steam inlets100 to condensate outlet 104.

[0080] Although depicted with the steam being directed into the innershell 88 and the liquid desiccant being directed into the chamber 92,the opposite arrangement may be employed with the liquid desiccantdirected into the inner shell 88 and the steam delivered to the chamber92. FIG. 15 illustrates an alternative embodiment of a condenser 86 aincluding a housing 90 a and inner shell 88 a, wherein the inner shell88 a segregates housing 90 a into two compartments 92 a, 92 b,respectively. A steam inlet tube 100 a communicates with compartment 92a, and a steam inlet tube 100 b communicates with compartment 92 b.Partially heated dilute desiccant solution is delivered to inner shell88 a through solution inlet 108 a, and is sensibly heated by the latentheat of condensation as the steam condenses in the respective chambers92 a, 92 b. Condensate flows out of chambers 92 a, 92 b, via condensateoutlets 104 a, 104 b, respectively. Partially heated dilute desiccant atthe second temperature flows out of inner shell 88 a through solutionoutlet 110 a to coiled interchange heat exchanger 58. Baffles 112 a, 112b are provided in chambers 92 a, 92 b, respectively.

[0081] Referring to FIG. 16, a third embodiment of a condenser 86 b isillustrated that includes a housing 90 b and a plurality of tubes 118which may be convoluted or corrugated as described above with regard tothe interchange heat exchangers and shown in FIGS. 12A and 12B. Thetubes 118 are supported by opposing support plates 120 and communicatewith respective steam inlets 100 c, 100 d through which steam isdelivered from boiler 34. The housing 90 b includes a liquid desiccantsolution inlet 108 b to receive dilute liquid desiccant from splitinterchange heat exchanger 66, and an outlet 110 b to deliver partiallyheated liquid desiccant at the second temperature to the coiledinterchange heat exchanger 58. The tubes 118 are preferably fabricatedfrom Teflon, and the support plates 120 include at least one siliconerubber sheet attached thereto.

[0082]FIG. 17 illustrates another embodiment of a condenser 86 cutilizing multiple double-pipe heat exchangers. Each double pipe heatexchanger includes an outer straight tube 300 and an inner convolutedtube 302 concentrically disposed within the outer tube. A small annulargap is defined between the outer and inner tubes 300, 302 which forcesthe fluid to follow a “screw-like” tortuous path through theconvolutions at high velocity. This arrangement provides high heattransfer coefficients and condensation capacity. The components can befabricated from plastics such as polypropylene, Teflon, PVDF or siliconerubber. Dilute liquid desiccant from split Interchange heat exchanger 66is directed into a manifold 304. Similarly, steam from boiler 34 flowsinto a manifold 306 through inlet ports 308. Manifold 304 communicateswith the inner convoluted tubes 302. Steam flows through the annuliformed between outer tubes 308 and inner tubes 302 causing the diluteliquid desiccant entering the heat exchangers from manifold 304 to bepartially heated to the second temperature. This heated liquid desiccantis delivered to the coiled interchange heat exchanger 58 from exitmanifold 310. Condensate is collected in manifold 312, and is thendelivered to pan 106. Air vents are utilized to ensure reliable gravityassisted drain flow of the liquid desiccant from the absorber 12 to theboiler 34. Small pieces of Teflon tape having a micro-pore structure canbe used in the vent assembly. The Teflon material is hydrophobic and hasa micro-pore structure which enables the free passage of air whilepreventing steam or desiccant leakage. The air vent 314 includes a tube316 extending upwardly from manifold 310. The tube 316 includes apolypropylene mesh 318 and a piece of Teflon tape 320 in a laminatedstructure. Alternatively, conventional float-based air vents, such asair vents manufactured by Honeywell, can be utilized to vent air fromthe system.

[0083] Referring to FIG. 18, another embodiment of the condenser 86 dcomprises multiple coiled double pipe heat exchangers. Each double pipeheat exchanger includes an outer helically coiled cylindrical tube 300 aand an inner convoluted tube 302 a concentrically disposed within theouter tube 300 a. Steam from boiler 34 enters a manifold 306 a, fromwhere it is communicated into the annuli formed between outer tubes 300a and inner tubes 302 a. Dilute liquid desiccant is delivered tomanifold 304 a and thence into the inner tubes 302 a. Partially heatedliquid desiccant exits into manifold 310 a, and is delivered to coiledInterchange heat exchanger 58. Condensate flows through outlets 312 a topan 106. This condenser 86 d, operates on the same principles and offersthe same advantages as the double-pipe condenser 86 c described above.

[0084]FIG. 20 illustrates the respective components of the LDA 10 instacked relation within frame 35 (the components of the absorption airconditioner 202 are not shown).

[0085] During the operating cycle, ambient air is drawn into the unit,through absorber 12 and exhausted to the room by fan 23. The moisture inthe air is extracted as the air makes contact with the liquid desiccantwicking across the microglass fiber wick plates 20, 22. Dilute liquiddesiccant is gravity fed from drain pan 24 of absorber 12 to manifold 76of split interchange heat exchanger 66, wherein it is raised to a firsttemperature through heat transfer from concentrated liquid desiccantflowing through annuli 74. The dilute liquid desiccant at the firsttemperature is then delivered to the condenser 86, in which the latentheat of condensation as the steam condenses sensibly heats the liquiddesiccant to the second temperature. The liquid desiccant at the secondtemperature is thereafter delivered to the coiled interchange heatexchanger 58 in which it is further heated to a third temperature priorto introduction into boiler 34 for regeneration. The coiled interchangeheat exchanger 58 recovers waste heat radiating from the walls 36 ofboiler 34. The concentrated liquid desiccant solution produced byboiling the liquid desiccant is drawn through the coiled interchangeheat exchanger 58 and split interchange heat exchanger 66, andthereafter delivered to distributor 14 of absorber 12 by pump 80. Thestacking of the respective components as shown in FIG. 8 provides forthe gravity feed of dilute liquid desiccant from absorber 12 to boiler34 through the first and second heat exchangers and the condenser,thereby eliminating the need for multiple pumps in the system.

[0086]FIG. 21 illustrates a liquid desiccant dehumidifier, indicatedgenerally at 450, wherein components which are similar to those employedin the aforedescribed liquid desiccant dehumidifier 200 have commonreference numerals. The liquid desiccant dehumidifier, which mayhereinafter be referred to as the dehumidifier 450, is operative todehumidify incoming ambient air prior to effecting sensible cooling ofthe air in an air absorption air conditioner, such as the aforedescribedair conditioner 202. In similar fashion to the liquid desiccantdehumidifier 200, the dehumidifier 450 includes an absorber 452, acondenser 454 and a boiler 456 which are supported in generallyvertically stacked relation above a condensit pan 106. As will bedescribed, the boiler 456 includes a coiled interchange heat exchanger458 disposed between the boiler 456 and condenser 454. A splitinterchange heat exchanger 66′ is disposed between the condenser 454 andthe absorber 452. As with the aforedescribed embodiments of the liquiddesiccant dehumidifier 200, liquid desiccant drains from the absorber452 to the boiler 456 through the split interchange heat exchanger 66′and condenser 454 by gravity. A pump 80 is operative to drawconcentrated desiccant from the boiler at a relatively high temperaturethrough the heat exchanger 66′ and pump the concentrated desiccant intothe absorber.

[0087] Referring to FIGS. 22 and 23, taken in conjunction with FIG. 21,the liquid desiccant absorber 452 is operative to absorb moisturecontained in ambient air entering the dehumidifier 450. In similarfashion to the aforedescribed desiccant absorber 12, the absorber 452 isconstructed and arranged for receiving concentrated liquid desiccant atthe top of the desiccant absorber and dispensing dilute liquid desiccantfrom the bottom of the absorber. The desiccant liquid may comprise aconventional desiccant solution as aforedescribed.

[0088] In the embodiment illustrated in FIGS. 22 and 23, the absorber452 includes two horizontally arranged generally equal length rows orstacks 462 a and 462 b of relatively closely spaced vertically disposedmicroglass fiber plates 464 which are preferably of substantially equalrectangular size and thickness, although the size and thickness of theplates may be varied and need not be equal. The fiber plates 464 aresupported by a suitable frame structure so that each of the plates inrow 462 a is generally coplanar with a corresponding plate in row 462 band so that the laterally opposite vertical marginal edges of the fiberplates in each row lie in common substantially vertical planes, asrepresented by the outer marginal edges 464 a and the rearward marginaledges 464 b, respectively, on the row of plates 462 a shown in FIG. 22.

[0089] As shown in FIG. 22, the rows of microglass fiber plates 462 aand 462 b are disposed in parallel spaced relation so that a gap orspace 466 is provided between the exposed mutually opposed parallel rowsof plates. A top plate 468 of rectangular plan configuration issupported on the support frame for the fiber plates 464 so as to overliethe upper marginal edges of both rows 462 a and 462 b of fiber plates464. The plate 468 is also made of a microglass fiber material andserves as a distribution sheet to distribute concentrated desiccantintroduced into the top plate through a pair of input tubes 470 and 472which have discharge ends located, respectively, generally centrallyover the rows 462 a and 462 b of fiber plates 464. The desiccant inputtubes 470 and 472 are connected, respectively, to the pump 80 as shownin FIG. 21 so as to receive concentrate desiccant drawn from the heatexchanger 66′.

[0090] In operation, air is drawn through the absorber 452 by the fan 23in a direction normal to the plan of the coplanar vertical marginaledges of the fiber plates 464 so that moisture in the air is removed asthe air makes contact with the liquid desiccant that has wetted thefiber plates. As the desiccant dehumidifies the air stream, the moistureabsorbing capability of the desiccant is reduced and the diluteddesiccant is collected in a drain pan 474 similar to the aforedescribeddrain pan 24. A drain tube 474 a extends from the lower wall or bottomof the drain pan 474 and includes a one-way or check valve preventingreverse flow into the absorber. By separating the rows or stacks 462 aand 462 b of microglass fiber plates 464 so as to create a verticallyoriented gap 466 between the stacks of plates, the air passing betweenthe stacks of fiber plates intermixes in the gap as the air flowsbetween the respective stacks of fiber plates. This intermixing, whichmay alternatively be termed passive mixing or remixing of the air beforeit enters the second row or stack of plates, improves the airdistribution and reduces channeling or short circuiting as the airtraverses the absorber. This improves the distribution of the masstransfer driving force and increases the mass transfer coefficient withresulting increase in capacity of the absorber. This arrangement alsoenables the area of the fiber plates to be reduced, thereby reducing theamount of desiccant residing in the plates with a correspondingreduction in cost. It will be understood that the absorber 452 mayinclude more than two parallel rows of fiber plates 464 which are spacedfrom each other so as to create a mixing gap between each pair of platerows. The absorber 452 may be employed in any of the dehumidifiersystems schematically shown in FIGS. 1-7.

[0091] Referring to FIGS. 24-26, taken in conjunction with FIG. 21, theboiler 456, which also may be employed in the various liquid desiccantdehumidifier systems illustrated schematically in FIGS. 1-7, includes arelatively narrow elongated generally U-shaped housing or vessel 480that includes a lower reservoir or trough-like portion 482 and a topplate 484 adapted to be releasably seated within the lower portion 482.The lower housing portion 482 is of generally U-shape in transversecross-section, as shown in FIG. 26, and defines an internal flow channelor passage 482 a adapted to receive liquid desiccant from the condenser454. To this end, a desiccant inlet tube 486 communicates with an inletend of the internal channel 482 a to facilitate the introduction ofdesiccant into the internal channel. An outlet port or tube 488communicates with the opposite outlet end of the channel 482 a tofacilitate withdrawal of heated concentrated desiccant from the channelafter it has passed from the inlet to the outlet. A heating element 490,which may take the form of an electrical heating element or coil, or agas fired heat tube, is disposed within the lower region of the channel482 a for heating liquid desiccant introduced into the inlet 486 andpassing through the channel to the outlet end 488. A plurality of steamoutlet ports 492 are spaced along the length of the upper top plate 484to facilitate discharge of steam to the condenser 454.

[0092] Referring particularly to FIG. 24, the interchange heat exchanger458 is connected to the desiccant end inlet 486 and outlet end 488 ofthe boiler 480. The heat exchanger 458 is operative to receive dilutedesiccant from the condenser 454, pass the dilute desiccant into theboiler inlet end 486, and receive the heated concentrated desiccant fromthe outlet end 488 of the boiler for passage to the inlet 78 of the heatexchanger 66′ from which the concentrated desiccant is pumped into theabsorber 452. To this end, the heat exchanger 458 includes a pair ofinner and outer coaxial flow tubes 498 and 500, respectively, thatdefine an annular flow passage therebetween operative to receive dilutedesiccant from the condenser. The coaxial tubes 498 and 500 arehelically wound or coiled internally of the generally U-shaped boiler480 with the outer tube 500 being connected to the boiler inlet end 486and the inner flow tube 498 being connected to the boiler outlet end488. Conversely, the inner flow tube 498 may be connected in flowcommunication with the boiler inlet end 486, and the outer flow tube 500connected to the boiler outlet end 488.

[0093] By providing a relatively long flow path within the boiler 480for the dilute desiccant to traverse from the inlet to the outlet,highly efficient heating of the desiccant takes place without mixingcaused by boiling of the desiccant as it passes from the boiler inlet tothe boiler outlet. As the desiccant flows from the inlet or cold end ofthe boiler to the hot or discharge end 488, the desiccant is heated,boiled and concentrated. This arrangement reduces the mass of thedesiccant that otherwise has to be maintained at the highest temperaturein the boiler, thereby increasing energy efficiency.

[0094] Referring to FIGS. 27 and 28, taken in conjunction with FIG. 21,the condenser 454, which may also be employed in the various liquiddesiccant dehumidifier system of FIGS. 1-7, includes a pair of parallelspaced generally vertical walls in the form of generally oval shapedinner and outer walls 506 and 508 interconnected at their lower marginaledges by a bottom wall (not shown) so as to establish an endless flowpath within the condenser. This flow path receives steam through a pairof steam inlets 510 connected in flow communication with the steamoutlets 492 on the boiler vessel 480. The steam passage defined betweenthe walls 506 and 508 is closed on its upper end by a suitable top wall512 (removed from the condenser shown in FIG. 27).

[0095] A convoluted or corrugated flow tube 514, such as illustrated inFIGS. 12A or 12B, is positioned within the steam path defined betweenthe walls 506 and 508 of the condenser 454 and has an inlet end 514 aconnected to the heat exchanger 66′ so as to receive desiccant from theheat exchanger 66′. The corrugated flow tube 514 has a desiccant outletend 514 b that is connected to the annular flow path defined between thecoaxial tubes 498 and 500 of the heat exchanger 458.

[0096] The convoluted desiccant flow tube 514 preferably contacts atleas one of the condenser walls 506, 508 so as to improve heat transferfrom the steam to the convoluted tube. Use of a convoluted tube 514 alsoprovides greater flexibility and provides larger heat transfer area withresulting improved heat transfer to the desiccant flowing through thetube 514. It will be understood that while the condenser walls 506, 508are illustrated as being generally oval in configuration, they coulddefine a circular or generally square steam passage housing thedesiccant flow tube 514. Moreover, more than two concentric walls couldbe provided providing a plurality of parallel channels or paths each ofwhich has a convoluted tube therein for effecting increased heattransfer to desiccant flowing through the convoluted tubes.

[0097] While preferred embodiments of the present invention have beenillustrated and described, it will be understood that changes andmodifications may be made therein without departing from the inventionin its broader aspects. Various features of the invention are defined inthe following claims.

What is claimed is:
 1. A boiler for heating dilute liquid desiccant andevaporating moisture so as to reconstitute the liquid desiccant intoconcentrated liquid desiccant, said boiler comprising a vessel definingan elongated flow channel having adjacent one end an inlet adapted toreceive dilute liquid desiccant therein and having adjacent an oppositeend an outlet enabling discharge of liquid desiccant, a heating elementdisposed within said flow channel operative to effect progressivelyincrease temperature heating of the liquid desiccant passing from saidinlet end to said outlet, and at least one steam port operativelyassociated with said vessel so as to release steam generated by heatingsaid liquid desiccant.
 2. A boiler as defined in claim 1 wherein saidvessel is generally U-shape in plan configuration, said inlet and outletends of said flow channel being disposed at opposite ends, respectively,of said U-shape.
 3. A boiler as defined in claim 1 in combination withan interchange heat exchanger having a pair of coaxial tubes defining atleast two flow passages disposed in concentric relation, one of saidflow passages being in flow communication with said inlet end of saidflow channel, and the other of said flow passages being in flowcommunication with said outlet end of said flow channel.
 4. Thecombination as defined in claim 3 wherein said coaxial tubes have atleast a portion of their length disposed in a helically coiled relationdisposed in generally coplanar relation with said vessel.
 5. Thecombination as defined in claim 4 wherein said vessel is generallyU-shaped in plan configuration, said helically coiled portion of saidheat exchanger being positioned between leg portions of said U-shapedvessel.
 6. An absorber for removing moisture from a gas passed throughthe absorber, said absorber comprising at least two stacks of microglassfiber plates, each of said stacks including a plurality of generallyplanar microglass fiber plates disposed in generally verticalhorizontally spaced relation, said stacks being disposed in mutuallyopposed parallel spaced relation so as to define a gap therebetween, adispensing plate supported in generally overlying relation to saidstacks and operative to receive a concentrated liquid desiccant anddispense said desiccant onto said vertically disposed plates so as towet said plates, and a drain pan disposed below said plates to receivemoisture removed by said wetted plates from said gas passed through saidabsorber in a path to effect contact with said plates, said gapeffecting mixing of said gas as it passes through said gap between saidstacks.
 7. A condenser for sensibly heating a dilute liquid desiccant bysteam said condenser comprising at least two concentric generallyvertical walls defining a flow passage therebetween, at least one ofsaid walls having at least one inlet communicating with said flowpassage to enable steam to be introduced into said flow passage, and aflow tube disposed within said flow passage and having opposite inletand outlet ends intersecting at least one of said walls to enable entryof liquid desiccant into said flow tube so as to effect heating of saidliquid desiccant by said steam.